Electromagnetic wave transmission system



NOV. 26, 1946. G, BUSlGNlES 2,411,518

ELECTROMAGNETIC WAVE TRANSMISSION .SYSTEM Filed April l2, 1943 7Sheets-Sheekl l TRA/vsh/rrf@ digg-1 #ECT/VER H. G. BuslGNn-:s 2,411,5l8-

ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM Filed April l2, 1945 7Sheets-Sheet 2 vm 1 All m. w V V Y Y V11 l# L/ L @A f o a w m u w d .d w

Nov. 26, 1946.

NOV. 26, 1946. H G- BUSlGNlEs k2,411,518

ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM Filed April l2, 1943 7Sheets-Sheet 3 OUTPUT Nov. 26, 1946.- H. G. USIG'NIES 2,411,518

ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM Filed April 12, 1945 7sheets-sheet 4 Nw. 26, 1945." H Q BUSIGNES www ELECTROMAGNETIC WAVETRANSMISSION SYSTEM Filed April l2, 1945 7 Sheets-Sheet 5 I N V EN TOR.HfA/// G. 505/611055' Nov. 26, l1946. H. G. BuslGNlEs u 2,411,518

ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM Filed April 12, 1945 '7shams-sheet e Dmmmnmm Fr-f INVENTOR. /ff/v/P/ G. sw/@M55 Nov. 26, 1946.H. G. BuslGNlEs 2,4l1,51

ELECTROMAGNETIC WAVE TRANSMISSION SYSTEM Filed ApIil 12, 1945` 7Sheets-Sheet '7 caMB//w/vs ,427

oEv/cE l OUTPUT IN V EN TOR.

WMNEY f Patented Nov. 26, 1946 mais ELECTROMAGNETIC WAVE TRANSMISSIONSYSTEM Henri G. Busignies, Forest Hills, N. Y., assignor toInternational Standard Electric Corporation, New York, N. Y., acorporation of Delaware Application April 12, 1943, Serial No. 482,677

In France May 27, 1942 19 Claims.

The present invention relates to electromagnetic wave transmissionsystems, and in particular to systems such as transmitter systemswherein a transmitted wave is characterized by having a spectrum offrequencies, the frequencies varying with different directions ofpropagation, and/or receiver systems wherein the frequency of a receivedwave may be translated to other frequencies depending upon the directionof wave propagation with respect to a receiving system.

In a general way, the wave transmission systems provided for in thepresent invention are characterized by the fact that they not onlypermit the radiation of waves having frequencies dierent from thefrequency of the oscillations which produce the waves, but also permitin the case of reception, a frequency translation of received waveswhereby the frequencies of currents in the receiver circuits aredifferent from those f observable in the vicinity ef the receivingequipment,'and to which the receiving antennas are tuned.

The transmission systems provided for in the present invention alsocomprise means for making the frequency of a transmitted wave dependentupon the angle of radiation from a transmitter on the one hand, and formaking the frequency of a received wave on the other hand dependent uponthe angle of incidence which the wave makes with a receiving system.

The processes for establishing wave transmission systems such as thosedefined above are such that the frequencies of the radiated or thereceived waves are different from those frequencies which are created inthe circuits of the transmitting or receiving apparatus as the case maybe, and vary in a manner dependent upon the direction of the propagatedwave with respect to a predetermined axis of either a transmitting orreceiving antenna array.

- in accordance with one feature of my invention, means may be providedat a transmitter for modifying the radiation from a group oftransmitting aerials in such a way that the radiation successively hasas a center, a different aerial of the group. Similarly, in accordancewith another feature of my invention, means may be provided at areceiver for successively intercepting energy from a different aerial ofa group of receiving aerials. The angular variation of phase, andconsequently the variation in frequency, as well as the directivity ofthe aerial systems depends on the rapidity at which the aerials of agroup of aerials successively perform their radiating or receivingfunction.

The transmission and reception features of my invention may best'beexplained by rst considering the Doppler-Fizeau principle. Consider, forexample, a radiating antenna moving through space at high velocity. Inaccordance with the Doppler-Fizeau effect the result would be thatl aspectrum of waves-varying in frequency would exist in space. The wave ofmaximum frequency would be in the direction toward which the antenna wasmoving and the wave of minimum frequency in the opposite direction. Therate of angular frequency variation in azimuth would be dependent on thevelocity of the moving antenna. If a receiver were suiciently selective,it could detect small frequency variations and therefore small angularvariations.

If, in a unit of time, a transmitting antenna is moved toward areceiving antenna by a distance nl, the Wave frequency appearing at areceiving antenna will have been increased by n periods during the unit`of time. If the transmitting antenna had moved in the opposite diirection or directly away from the receiving antenna, the wave frequencyat the receiving antenna would have been decreased by n periods.

Similar phenomena would also take place if the transmitting antenna werestationary and the receiving antenna were moved to and from thetransmitting antenna. However, in both of these cases the frequencywould not have varied at all if one of the antennas had been moved on acircumference centered on the other antenna orin a directionperpendicular to the direction dened by the two antennas provided thedisplacement or total antenna motion was small with respect to thedistance between the antennas. If the direction of motion of one of theantennas is at an angle to the direction defined by the antennas, therewill be a change in frequency determined by the cosine of the angledetermined by said two directions. Let 0 be the acute angle between thedirection of the displacement and the direction in line with the twoantennas. kIi' the displacement amounts to nl in a unit of time, one ofthe antennas will have moved with respect to the other by m cos 0, andthe received or transmitted frequency will have varied by 1LT cos 0where T is the period of one cycle. When the cos 0 is positive, thefrequency will have increased; and when the cosine is negative thefrequency will have decreased.

Obviously it is impossible to physically move an antenna at a velocitywhich would produce a neasuralble Doppler effect, but in accordance yithmy invention, I produce by electrical means ihe effect of an antennamoving with great ve- Locity.

The equivalent of a rapidly moving antenna provides means for producingseveral novel communication systems, direction finding systems, beacons,etc. For example, in distinction to known forms of direction findingsystems wherein direction determination is effected by direction finderswhich select radio waves of one constant frequency as the result of theorientation of a directive aerial system, the equivalent of a. rapidlymoving antenna Provides a means for determining direction by a selectionof frequency. In general, in transmission systems embodying an` an..tenna having the above described characteristics, several transmissionsthat are made on the same frequency but which come from differentdirections, or portions of a single transmission that arrive overdifferent spacial paths, will appear to the receiver as if they haddifferent frequencies, thus permitting the picking up and the selectingof these various transmissions according to their directions ofpropagation.

In the following I have enumerated' several objects of my inventionnamely:

l. To provide a method of wave transmission or reception, as the casemay be, which comprises electrically producing the effect of an antennamoving rapidly through space;

2. To provide an antenna array wherein the aerials thereof are energizedsuccessively from one end of the array to the other end thereof;

3. To provide a wave transmission system in which the frequency of theradiated wave in space varies with different directions of radiation;

4. To provide a wave transmission system by which a determination ofVdirection may be made by frequency selection.

5. To provide a wave transmission system wherein the apparent frequencyof a carrier Wave may be varied at the receiver;

6'. Toprovide a radio beacon system wherein various courses may bedetermined by the beats produced from a plurality of radiations ofvariable frequency.

7. rTo provide a radio direction finding system wherein the sense ofdirection is determined by frequency selection;

8. To provide for the elimination of polarization errors in radio.direction finders;

9. To provide. a communication system wherein by the transmission ofwaves of different frequencies at different angles in the vertical planethe quality of reception is greatly improved.

l0. To provide radio transmitters which are difficult to locate byltriangulation methodsY withY direction finders; and

ll. To provide a receiving system which is free from polarizationerrors.

Other objects, features, capabilities and advantages of my inventionwill appear from the following detailed description taken in connectionwith the accompanying drawings showing several illustrative embodimentsand wherein:

Fig. 1 is a schematic representation of a wave transmission system forillustrating a principle of my invention;

Fig; Z'is av series of'vector diagrams illustrating the operation of'myWave transmission system;

Fig. 3 is a schematic circuit diagram illustrating the operation andenergization of a transmitting antenna array inaccordancevvvth .myinvention;

Fig. 4 is a schematic circuit diagram of a portion of Fig. 3 modifiedfor illustrating how the antenna system of my invention may be employedfor the reception of radio waves;

Fig. 5 illustrates a series of electrical voltage waves for controllingand regulating the radiation from, orv in general the conditioning of,the various individual antennas of my antenna array;

Fig. 6 illustrates schematically a radio beacon system in accordancewith my invention;

Fig. 7 illustrates schematically a direction finding system comprisingthe wave transmission system in accordance with my invention;

Fig. 8 is a block diagram illustrating a two course beacon comprisingcrossed antenna arrays:

Fig. 9rk is a block diagram illustrating a communication system forreducing the effects of fading in accordance with my invention; and

Fig. l() is a block diagram illustrating a second type of communicationsystem for reducing the effects of fading in accordance with myinvention.

Referring iirst to Fig. 1, the transmitter 'I' and the receiver Rrepresent a communication system. The transmitter may be of any type andradiates a carrier wave represented by the reference character W. 'Ihereceiver R may be of any type suitable for receiving the type of wave Wand is assumed to be capable of moving at high velocity in the directionof the arrow which is at an angle 0 with the direction joining thetransmitter and the receiver. If the angle 0 were zero and the receivingaerial were moved directly toward the transmitter, in a unit of time itwould have travelled a distance nk and the received frequency would havebeen increased by n periods per second. On the other hand', if thereceiving aerial had moved directly away from the transmitter, thefrequency would have been diminished by n periods in a unit of time. Ifthe receiver were moved in the direction of the arrow 0 having a finitevalue, the received frequency would have been varied in a unit of timeby the value 11T cos 0 Where T is the period of one oscillation. If thecosine of 0 were positive the frequency would have been increased and ifthe cosine of 0 were negative the frequency Would have been increased.

Remarks similar to the abovev could be made if it were assumed that thereceiving aerial was fixed and the transmitting aerial was moving. Thesame formulas willhold true in either case wherein 0 represents theangle between the direction of the moving aerial and the directionrepresented by the line between the transmitter and the receiver.

It is obvious that neither a transmitting nor a receiving aerial can bemoved rapidly through space .but in Fig. 2 I have diagrammaticallyillustrated how a transmitting antenna consisting of an array of aerialsin accordance with my invention will produce the same result as if atransmittingv aerial were actually physically moved through space.

Referring now to Fig. 2, the numerals l, 2, 3, l and 5. representindividual fixed aerials of a five aerial array. A receivingy aerial 9is located at a distance from the aerial array.. In order to illustratethe operation of the array the separation of the aerials thereof. havebeen given predetermined valuesand for simplicity of discus-r sion theseparation has been chosen as a quarter wavelength at the operatingfrequency. All of the aerials are conditioned so that they will radiatein phase for a predetermined time period 5 which will be furtherexplained hereafter. Let us further assume that the magnitude of theradiated wave as radiated from a single antenna varies in accordancewith the positive half of a sine wave and that no more than two adjacentaerials are radiating simultaneously.

In accordance with my invention at zero time, as noted on the time scaleat the left of Fig. 2, antenna I is radiating a, wave of maximumamplitude and is represented by the vector V1. At the remote receivingaerial 9 the Vector of the received Voltage is represented by V2. Thephase relationship between V1 and V2 may be of any value whatsoever butI have illustrated them both as being in the same direction or phasewhich would correspond to the condition in which there were an evennumber of wavelength between the transmitting and receiving antennas.The vector f the received voltage would be a maximum at the same timethat the transmitter was radiating at maximum amplitude at somesubsequent period, this period being equal to the time required by theradiated wave to travel between the transmitter and the receiver. Atzero time the radiation from antennas 2, 3, 4 and 5 is zero.

As above mentioned, the radiation from each antenna is modulated inaccordance with the positive half of a sine wave, the modulating wavesfor each antenna being displaced in phase by 90 for adjacent antennas.In other words, when the radiated wave from one antenna is a maximum,the radiated wave from an adjacent antenna is zero. Again referring toFig. 2, vectors Va and V4 represent the values of the radiated wavesfrom antenna l and 2, respectively, as they would exist at a time equalto one-eighth of a cycle of the modulating wave following the time zero.This is equivalent to a 45 phase displacement of the modulating voltage.The vector V1 would have decreased to a value of 0.707 of its originalvalue. Vector V4 would have increased from zero to a value of 0.707 ofits maximum value.

Although there has been a phase rotation of 45 during this period, Ihave represented vectors V1 and V3 in the same direction for simplicityof disclosure and since the main object of this iigure is to illustratethe manner in which the voltage vector at the receiver is displaced inphase. At the time T/8 when V3 is equal to 0.707 of V1 the voltagevector V5 at the receiver has also been reduced to 0.707 of its maximumvalue. The voltage vector V6 at the receiver represents the magnitudeand phase relation of the energy re` ceived from antenna 2. It will berecalled that all antennas, when radiating, are radiating in phase andsince antenna 2 is closer to the receiver by a distance equal toone-fourth wavelength of its radiated wave, the energy from antenna 2arrives at the receiver one-fourth cycle in advance of the energyreceived from antenna l. This accounts for the 90 advance phase relationof vector V6 with respect to vector V5. The result out of V5 and Vs isrepresented by V7. It

will be observed that V1 has advanced one-eighth` An eighth of amodulation cycle later, the current in antenna 2 has decreased to 0.707of its maximum value as represented by vector V10 and at this time theradiation from antenna 3 represented by vector V11 has increased fromzero to 0.707 of its maximum value. The current in antenna l remainszero since it will be recalled that the antennas are only radiating onthe positive halves of the modulation cycle. The vectors V12 and V13 atthe receiver correspond to the vectors V10 and V11 at the transmitterand their resultant vector V14 illustrates the fact that another advanceof one-eighth cycle has taken place and that the maximum value hasremained unchanged.

It is not believed necessary to continue with a detailed discussion ofthe vectors as they would occur during following time period-s. It willbe seen, however, that for a complete cycle of the modulating wave theresultant vector at the receiver has rotated 360 or one revolution in aforward direction. 'Ihis is equivalent to increasing the frequency atthe receiver by one cycle. If the time period of a single cycle of themodulating wave is taken very small, for example, twenty microseconds,there would be 50,000 rotations of the resultant voltage vector at thereceiver every second.` This would correspond to an apparent increase infrequency at the receiver of 50 kilocycles or the frequency of thereceived wave would be 50 kilocycles greater than the carrier waveradiated by the antenna-s 1 to 5 individually.

Refer now to Fig. 3 wherein I have illustrated my invention as embodiedin a transmitter consisting of eight antennas in a lineal array togetherwith control apparatus for their energization. The antennas l, 2, 3, 4,5, 6, l, and 8 are separated one from the other, a distance equal toone-quarter wave length of the frequency at which they are designed toradiate. The complete array therefore covers a distance of one andthree-quarters wave lengths. This spacing is by way of example only andother spacings may be employed as explained more fully hereinafter.

Connected to antenna l is control device l0, which I have illustrated asa vacuum tube having a cathode, an anode, and three grid electrodes.Similar control devices Il to l1 are connected to antennas 2 to 8respectively. Anode potential for the devices is derived from a sourceI8 illustrated as a battery. Choke coils 20 to 26 are connected betweenthe antennas as illustrated in order to isolate the antennas for radiofrequency currents. High impedance circuits could be employed in placeof choke coils if desired. Choke coil 21 isolates the power supply fromthe antenna 8. A high frequency source is illustrated by the block 29.This source may be of any type suitable for delivering high frequencyenergy to the grids 30 to 31 of control devices i0 to I l respectively.The voltages applied to grids 30 to 37 are in-phase one with the otherand this condition may be o-btained, for example, by making the 'lengthsof the transmission lines 40 to 41 all equal. If transmission lines arenot employed for connecting the high frequency source to the grids ofthe control devices, other known forms of obtaining in-phase voltagesmay be employed. In .accordance with my invention as illustrated in Fig.3, the antennas l to 8 are caused to radiate lsuccessively in thefollowing manner. A plurality of modulating sweep voltages operate onother grids associated with the control devices I0 to l'i in such amanner that the initiation of radiation in an antenna follows theinitiation of radiation in an adjacent antenna by a time period equal toone-quarter cycle of the modulating sweep voltage. In Fig. 3 it isassumed that the initiation of radiation from antenna 2 follows theinitiation of radiation from antenna l and that the initiation of energyin antenna 3 follows the initiation of energy in antenna 2 and so forththroughout the complete array. The term modulating sweep voltages isused since these voltages determine the rapidity with which the antennasare energized in sequence. The control circuits for controlling theinitiation of radiation in the antennas are such that radiation takesplace only during the positive halves of the modulating sweep voltagewaves as will be more fully explained hereinafter.

In accordance with my invention as illustrated in Fig. 3 not more thantwo antennas should radiate at the same time. To prevent thesimultaneous radiation of more than two antennas further blocking orconditioning control voltages are applied to an additional set of gridsin control devices l to il. rlhe conditioning voltages are applied togrids 50 to 51, and the modulating sweep voltages are applied to thegrids 110 to 41 of the control devices I0 to l1 respectively.

In order to more clearly illustrate the operation of my invention, themethod of obtaining the modulating and the blocking o-r conditioningvoltages and the manner in which they are generated and applied to thecontrol devices will now be described.

Take, for example, the numerical illustration given in connection withFig. 2 wherein the time period of the modulating sweep voltage wastwenty microseconds. Since each antenna is energized every quarterperiod of the modulating sweep voltage cycle, the initiation ofradiation from one antenna will follow that of the other by one-quarterof twenty microseconds or ve microseconds. This corresponds to amodulating frequency of fifty kilocycles per second. Conditioningvoltages having a period twice that of the modulating voltages are alsorequired. This is equivalent to a conditioning voltage frequency of 25kilocycles per second. It is convenient to first generate theconditioning voltage and to then. obtain the modulating sweep voltagefrom the second harmonic of the conditioning voltage. Four modulatingsweep voltages separated in phase by 90 are required in the presentillustration. Likewise four blocking or conditioning voltages arerequired. Two of these conditioning voltages have a phase displacementof 90 and the other two voltages have a phase separation of 180 from the90 phase related voltages. In Fig. I have illustrated the modulatingsweep voltages by curves A, B, C, and D and the conditioning voltages bycurves M, N, S, and T. The lower portion of Fig. 3 illustrates in blockdiagram the manner in which all of the various modulating sweep voltagesand the conditioning voltages are obtained. This portion of the diagramand the voltage curves of Fig. 5 are to be considered together. First, ablocking voltage M of 25 kilocycles is generated in any convenientmanner. In Fig. 3 the oscillator 6i! represents the generator of thisvoltage. A second blocking voltage N is obtained by passing the voltageM through phase shifter El wherein theY latter is retarded 90. A thirdblocking voltage S isolo-` tained by shifting the phase of the voltage Mby 180. This phase shift is accomplished by means of the phase shifter62. A fourth blocking voltage time sequence.

T is obtained by shifting the phase of voltage N 180 by the phaseshifter 63. Many forms of phase Shifters are well known in the art andrequire no detailed explanation as to their operation. The output of theoscillator is also passed through a frequency doubler B4 to form themodulating sweep voltage A. The latter voltage is passed through a phaseshifter 65 in which it is retarded to produce the voltage B and thevoltage D is obtained by shifting the phase of B by the phase shifter65. Voltage C is obtained from voltage A by shifting the phase of thelatter 180 by phase shifter El. It will be noticed in passing that thevoltages resulting from the 90 phase Shifters are retarded rather thanadvanced.

Rectiers lll, l5, '16, and 'Il have been included in the connectionsleading to various grids of the control devices. In the circuitarrangement for carrying out my invention illustrated in Fig. 3, theserectiers are not absolutely necessary a1- though they introduce noharmful results. They, however, are desirable in certain instances aswill be explained hereinafter. The characteristics of the controldevices of Fig. 3 are such that when the devices are conditioned foroperation, the potential on the grids 40 to 4l are in effect biasingVthe devices to cut-off, that is, current will flow in the variousantennas only when the positive half cycles of the modulating voltagesare applied. The grids and cathodes are in eiect functioning asrectiiiers and therefore the additional rectiers l-ll merely constituteother rectiers in series. However, there are types of control devicesother than those illustrated in Fig. 3 which could be employed, forexample, devices operating on the principle of balanced modulators. Incontrol devices of this latter type the use of rectifiers in theposition shown in Fig. 3 would usually be essential. The negative halvesof curves A, B, C and D have been shown in dotted lines to illustratethat these voltages are rectified.

Limiters 90, 9|, 92, 93 are placed between the blocking voltage sourcesM, N, S, and T and the grids 50-5 l 52-53, 541-55, and 55l respectivelyof control devices. These limiters limit the output voltage of theblocking voltages M, N, S and T to a value L illustrated by the dottedlines K in Fig. 5. The purpose of the blocking voltages is to socondition the control devices that the latter will be free to operateand permit wave energy to radiate from the antennas at certain times,and to prevent radiation from the antennas at other times, all inaccordance. with a predetermined The control devices havecharacteristics such that the limited blocking or conditioning voltagesin themselves contribute substantially nothing to the radiated waveenergy. The envelope of the modulated radiated wave is controlledsubstantially entirely by the modulating sweep voltages A, B, C, and D.The limiters are employed to reduce the large voltage peaks of theblocking voltages which otherwise might produce deleterious radiation.

The reason for originally giving the conditioning voltages a largeamplitude and then for reducing their amplitude by limiting is toproduce a voltage wave having relatively steep sides in order that theywill act on the control devicesv for substantially the complete cycle ofthe modulating sweep voltages,

Other types of conditioning voltages could also be employed. Forexample, a substantially square voltage wave having the shape of thecurve U as 9 shown in Fig. would be equally as eiective as the voltageM, N, S or T.

Considering now the time zero when antenna I is iirst conditioned toradiate. Voltage M is applied to grid 50 and voltage A is applied togrid 40. The voltage M unblocks or conditions the device IIJ and thevoltage A modulates the antenna current, the frequency of which iscontrolled by the high frequency voltage applied to the grid 30.

IAt this time the voltage M also unblocks control device I I, butcurrent is not radiated from the antenna 2 associated therewith sincethe modulating voltage B has not as yet been applied to the grid 4I ofthe control device. Similarly antennas 3 and 4 cannot radiate since themodulating voltages C and D have not as yet been applied to the grids 42and 43 of the control devices I2 and I3 respectively.

At zero time it will be seen that modulating voltage A is also appliedto the grid 44 of device I4 which is associated with antenna 5 onewavelength away from antenna I, and in the absence of preventive meansundesired radiation from antenna 5 would take place. To prevent thisradiation, the blocking voltage S is applied to the grid 54 of thedevice Ill.

A one-quarter cycle of the modulating voltage later, antenna 2 begins tcradiate since it is at this time that the modulating voltage B is rstapplied to the grid 4I. At this time, an antenna I is radiating atmaximum amplitude and antenna 2 is just beginning to radiate. None ofthe other antennas can radiate at this time since their associatedcontrol devices either blocked or the modulating waves have not as yetbeen applied to the grids of the control devices associated with theseantennas. Another one-quarter cycle later antenna 3 just begins toradiate due to the fact that modulating voltage C is just becomingpositive and the control device l2 has been unblocked by voltage N whichis also becoming positive. At this moment antenna 2 is radiating aloneat maximum output antenna l having discontinued to radiate. Anotherone-quarter cycle later antenna 4 begins to radiate and at this timeantenna 3 is radiating at maximum output.

An analysis of all of the control devices as they are being controlledin accordance with the voltages of curves of Fig. 4 would lead to theobservation that no more than two adjacent antennas of the antenna arrayare radiating at any one time, and also that the sum of the radiofrequency currents radiated by the array remain constant. However, aseach antenna of the array begins to radiate, the phase of the highfrequency wave is advanced one-quarter of a cycle. It will be seen thatthe frequency of the radio wave in space has been increased one cyclefor every sweep of a modulating sweep cycle voltage. As illustrated inFig. 3 the frequency of the radiated waves has been increased for areceiver located to the right of the figure and has been decreased for areceiver located to the left.

I have also illustrated in Fig. 3 a source of voltage represented -bythe block 80 for modulating the radiated current at, for example, avoice frequency. This modulating voltage is impressed on the anodes ofthe control devices through the transformer 8l. A frequency measuringdevice located at a distance to the right and in line with the antennaarray of Figure 3 would respond not to the frequency ofthe highfrequency source 29, but that frequency as modied by the frequency ofthe modulating sweep voltages. For example, in the numerical casepreviously taken, the frequency of the source 29 would be increased by50 kilocycles per second. A receiver located at this distant point couldtherefore be made selective to this increased frequency and of course,with suitable detecting apparatus, would reproduce the modulationoriginally placed on the carrier wave by the source 80.

While in the above description of the wave propagating system shown inFig. 3 I have assumed an antenna spacing of one-quarter wave length,this spacing was by way of example only.

With the one-quarter wave length spacing the required modulating sweepvoltages are four in number and differ in phase by 90. Other antennaspacing could also be employed. For example, if the antenna spacing weremade equal to one-third of a wave length, three modulating sweepvoltages would be employed diiering in phase by 120. In general thenumber of sweep circuit voltages required in any system is equal to thewave length of the high frequency source divided by'the spacing betweenthe antennas as measured in wave length.

In Fig. 4 I have illustrated a portion of a receiving antenna arraysimilar in character to the transmitting array shown in Fig. 3. I haveillustrated only two antennas and their associated apparatus in Fig. 4in order to avoid unnecessarily complicating the gure. In Fig. 4,antenna Ia is connected to ground through an impedance |50 and antenna2a is similarly connected to ground through an impedance I5I The grids30a and 3Ia of the two conditioning devices IIla and IIa are connectedacross the impedances I50 and I5I respectively. Modulating sweepvoltages are applied to grids 40a and IIa and blocking voltages areapplied to grids 50a and 5Ia. These voltages may be of the same type asillustrated by the curves of Fig. 5 and are applied to various grids ofthe conditioning devices in accordance with the circuit arrangementshown inthe lower portion of Fig. 3. For example, the modulating sweepvoltage A is applied to grid 40a, the modulating voltage B is applied togrid llla, and the blocking voltage M is applied to grids 50a and 5Ia. Asystem of this type is useful in providing the elect of a receivingantenna moving rapidly through space such as will be described later inconnection with Fig. 10. v

The above described wave propagation system may be employed incombination with other equipment to produce several new and novelresults. Fo-r example, in Fig. 6 I have illustrated a radio beaconformed by combining a wave propagation system such as shown in Fig. 3with a non-directional antenna to form a composite radiating system. Thewave propagating system comprises an antenna array composed of eightseparate antennas, a conditioning or control device connected to eachantenna, a modulating sweep voltage generator and a blocking voltagegenerator such as are illustrated in Fig. 3. The antennas and otherassociated conditioning and control means are illustrated in Fig. 6 bythe blocks I to 8, When an antenna array of this type is operating thecarrier wave is not of constant frequency for all directions from thearray but varies from a maximum to a minimum value, the maximum valuebeing in the direction in which the separate antennas are successivelyexcited and the minimum value in the opposite direction.

A separate antenna is positioned near the antenna array and isseparately excited at a frequency preferable between the maximum and l lminimumr frequencies of the carrier waves radi ated by the antennaarray. In Fig. 6 this separate antenna is shown as the block |06, andfor example it is excited at a frequency of cycles per second, theexcitation frequency for each antenna of the array being F, and thefrequency of the modulating sweep voltage being f.

At a distance from the array the carrier wave from the array and fromthe separate antenna combine or interfere to form beats. In thedirection shown by the arrow the frequency of a space wave from thearray is F-i-f and in the direction shown by the arrow |02, thefrequency is F-f. When these frequencies are combined with f F-l- 2 thefrequency of the separate antenna |00, the beat frequency in thedirection of the arrow ll is and in the opposite direction it is 11/21.At right the resulting beat frequencies at right angles to the array isin both directions.

The frequency of the carrier wave radiated from the array at an angle of60 from the direction shown by the arrow |0| is F+f cos 60 or lug Thisfrequency, which is radiated in the direction shown by the arrows |63and |04, would combine with the frequency the frequency of the waveradiated by the separate antenna |00, to form a resulting beat frequencyequal to zero.

A direction along which the beat frequency is zero could be employed asa course of a radio beacon. For example, an airplane ying this courseand having a receiver capable of receiving a band of frequencies F-i-fto F-f would indicate a zero beat while on the course, but a finite beatwhile off the course. Should the plane be off course, the pilot needonly y in the direction of lower beat frequency to arrive on the course.

The course or courses of any beacon may easily be changed in accordancewith my invention. All that is required is to vary the frequency thewave radiated by the yseparate antenna |00. For example, if thisfrequency is changed from the value Fig shown in Fig. 6 to a valueF-i-f, the beacon will armere 12 determine only a single course `andthis in the direction of the arrow Iil.

Principles, similar to those employed for defining the radio beaconillustrated in Fig. 6, may also be employed to provide a radio directionfinder such, for example, as illustrated in Fig. '7. In this figure, theantenna array and its associated apparatus are also illustrated by theblocks to 8. A separate antenna system and its associated controlequipment is illustrated by the block 0. All antennas are now to beconsidered as receiving antennas. The receiving antenna array ispreferably mounted in a manner such that it may be rotated through 360and is, therefore, capable of being orientated in any direction.

The problem now is to determine from what direction a signal wave isarriving. It may be arriving from any direction as illustrated in Fig. 7by the several arrows marked F. Actually the received signal is arrivingfrom only one direction and by rotating the receiving antenna array,this particular direction may be determined in the following manner. Avoltage from a modulating sweep voltage source is employed to sweepacross the antenna conditioning means associated with the antenna array.Let the frequency of the sweep voltage source be f. When the array ispointing toward the true source of signal having frequency F, theapparent frequency in the circuits of the receiver associated with theantenna array is F-l-f. This presupposes, of course, that the directionin which the antennas of the array are successively conditioned toreceive is toward the origin of the signal wave.

If the antenna array is not pointing toward the incoming signal, thefrequency developed in the circuits of the array receiver will be F--fcos 0, 0 being the angle between the direction of the incoming signaland the direction of the antenna array.

The non-directional receiver H0 also receives the wave having thefrequency F. In the receiver, this frequency F is also modulated by thefrequency f of the sweep voltage source with the result that a side bandfrequency F-i-f appears in the receiver output. The carrier frequency Fand the other side band F-f are suppressed.

The two frequencies F-i-f cos 0 from the array and F-l-J from theseparate receiving antenna are combined and detected in a detector ||2the output of which is equal to f-J cos 0. This frequency may beemployed to operate an indicator H3. It will be seen that when thedirection of the incoming signal and the direction of the arraycoincide, the cosine of 0 is equal to one and the frequency foroperating the indicator is equal to zero. Many forms of indicationcapable of indicating this condition of zero beat are known in the art.

From a study of Fig. it will be observed that there will be only onedirection in which this condition of zero beat occurs and therefore Ihave devised a direction finding system in which the well-known 180ambiguity of direction is not present.

In Fig. 8, I have illustrated a radio beacon system comprising twoantenna arrays and their associated equipment positioned at right anglesto each other. The antennas of each array are excited in phase at thefrequency F and are conditioned to radiate by modulating sweep voltagef. An analysis, in accordance with methods dis- Y cussed in connectionwith Figs. 6 and 7, of the beat frequencies occuring at a distance fromthe antenna arrays will showthat there will be two directions,v 180apart-in which the beati frequency will be zero. The Wave propagatingsystem illustrated in Fig. 8 would therefore be suitable for a twocourse beacon. Changing the modulating sweep voltage frequency of one ofthe arrays with respect to the modulating sweep voltage frequency of theother, will provide a means for changing the direction in which zerobeat will occur and therefore a means for changing the direction of thecourses.

Referring now to Fig. 9 I have illustrated a communication system inaccordance with my invention which provides a means for reducing theeffects of fading at a receiver. In the examples discussed above, it hasbeen tacitly assumed that the variation in carrier wave frequencyradiated at various angles to the antenna array occurred in thehorizontal plane.

Actually, of course, a wave of any given carrier frequency defines acone of revolution with the axis of the cone coinciding with thedirection of the array. This means, of course that the frequencyradiated from the antenna array of my invention varies in a verticalplane in the same manner that it does in a horizontal plane.

Considering now the antenna transmitting array and its associatedequipment shown by the block 300 in Fig. 9. Also assume thatthedirection in which the antennas of the array are successively energizedis in the direction H. Carrier waves having different frequencies willbe radiated in the vertical plane. If the frequency at which eachantenna of the array is excited is F, and the frequency of themodulating sweep voltage is .'f, as in the other illustrations hereingiven, the frequencies of the various waves in the vertical plane willbe F-l-f cos where 6 is the angle between the horizontal and thedirection in the vertical plane in which the carrier wave is propagated.

Somewhere in the upper atmosphere the various carrier1 waves arereflected and eventually arrive at a receiving point illustrated in Fig.9 as an antenna SID. The antenna is connected to a broad band receiver3| l, the band width of the receiver being sufficient to coversubstantially all of that portion of the frequency spectrum of thevarious carrier waves reaching the receiving antenna. A plurality offrequency selectors are connected to the wide band receiver forselecting those carrier frequencies which preferably contain the mostenergy. In the gure, I have illustrated two selectors only namely 3I2and 3|3, it being understood that as many selectors as desirable couldbe employed. To each frequency selector is connected a detector shown asblocks 314 and SI5. The detected outputs are combined directly and maybe amplified in the amplifier illustrated as block Slt. The output ofSES represents the desired signal.

Referring now to Fig. 10, I have illustrated a second type ofcommunication system employing the principle of an antenna movingrapidly through space. In contradistinction to the system illustrated inFig. 2 wherein the transmitter employed the antenna array of myinvention, the antenna array in Fig. 10 is employed at the receiver. InFig. 10 a transmitting antenna 400 is assumed to be transmitting a voicemodulated carrier wave to the receiving system All). The carrier wavemay take a plurality of paths, the wave along each path being reflectedin the upper atmosphere, and arriving at the receiving system at variousvertical angles. The carrier waves are all of the same frequency indistinction to their having different frequencies as described inconnection with Fig. 9.

As the carrier waves strike the receiver antennas at various angles,there is developed within the receiver a plurality of differentfrequencies depending upon the angle of reception and the periodicity ofthe modulating sweep voltage. The conditioning devices and controlcircuits therefore are illustrated by the block 4i l. All of thefrequencies developed are passed to a wide band amplifier illustrated bythe block 412. Fromthe wide band amplifier connections are made to aplurality of frequency selectors illustrated by the blocks M3, lllll,M5, and M6.

l. To each selector is connected a separate detector illustrated by theblocks 523, 624, 425, and Q25. The outputs from the detectors aredirectly combined in a combining device G21. The output from thecombining device represents the signal.

It is preferable that the selecting devices 443 to M6 select thosefrequencies which contain the most energy and this may be accomplishedby connecting to the wide band amplifier a scanning frequency receiverillustrated by block 428. The output of the scanning frequency receiveris connected to a cathode ray oscillograph 429 which will show all ofthe frequencies developed from the carrier wave by the receivingantenna,

and also the relative magnitudes at the variousV frequencies. Knowingthe frequencies having the greater magnitudes it is possible to adjustthe selectors M3 to M6 to select these frequencies for final detectionthereby obtaining maximum output.

It will be appreciated from a study of Figs. 9 and 10 and thedescriptions relating thereto that the communication systems illustrateddepend upon the principles of frequency selection in order to avoid theeffects of fading.

This method of overcoming fading is distinctly different from methodsemployed in the prior art which make use of either a plurality ofantennas geographically spaced or of very sharp directive receivingsystems.

It should be pointed out in passing that any transmitter employing theprinciples of my invention radiates waves the source of which is verydifficult to locate by triangulation methods. For example, a directionfinding system located at a distance from the source of waves willrespond only to a particular frequency depending on the angle betweenthe direction of propaga'- tion of the waves and the direction of theantenna array producing the waves. The direction finder can onlydetermine the line of propagation of the received waves. To determinethe exact location of the source of waves by triangulation methods,another direction finder must also determine the direction of wavepropagation of the received waves with respect to its position. However,the two direction finders, although taking bearings on the same wavesource, are actually receiving waves of different frequencies and unlesssome characteristic modulation is present in the waves, it will bedifficult for said direction finders to be sure that they aretriangulating on the same wave source.

While I have described above the principles of my invention inconnection with specific apparatus and in several modifications thereof,it is to be clearly understood that this description is-given only byWay of example and not as a limitation on the scope of my invention asset forth in the objects of my invention and the accompanying claims.

I claim:

i. An antenna Vsystem comprising a plurality of antennas arranged in apredetermined array, each of said antennas having substantially the sameradiation pattern, and antenna conditioning means connected to saidantennas to condition the same for successive wave translation in amanner simulating the effect of a single antenna together with itsradiation pattern moving through space.

2. A wave translating system comprising a plurality of antennas arrangedin a predetermined array, each of said antennas having substantially thesame radiation pattern, antenna conditioning means connected to eachantenna for conditioning said antennas to operate successively for wavetranslating purposes, and control means for timing the operation of saidconditioning means to initiate the conditioning of one of said antennaswhile discontinuing the conditioning of another of said antennas.

3. A directional wave propagating system for a predetermined wavelength,comprising a .plurality of antennas arranged in a predetermined array, ahigh frequency power source, said antennas being spaced apart a distanceequal to a predetermined fraction of the wavelength corresponding to thefrequency of said source, wave generating means including a power supplymeans connected to each of said antennas for energizing same atpredetermined time intervals, means connecting said source to saidgenerating means for conditioning said generating means to generatein-phase energy at said yfrequency, and control means connected to saidgenerating means for timing the radiation of said in-phase energywhereby each antenna radiates successively at said predetermined timeintervals to produce a wave in space having a length equal to saidpredetermined wavelength.

4. A directional wave propagating system in accordance with claim 3wherein said control means comprises a second Wave generating meanshaving a frequency equal to the difference in frequency between thefrequency corresponding to said predetermined wavelength and thefrequency of said power source.

5. A directional wave propagating system for a predetermined wavelengthcomprising a high frequency power source, a plurality of subordinateantenna arrays, each subordinate array comprising a plurality ofantennas, the spacing Vof antennas in each subordinate array being thesame, said subordinate arrays being arranged -in overlapping spacedrelation -to form Aa lineal main antenna array, the antennas of the mainarray being spaced apart a distance equal to a predetermined fraction ofthe wavelength corresponding to the frequency of said Source, wavegenerating means connected to each of said antennas for energizing sameat predetermined time intervals, means connecting said source to all oflsaid generating means for conditioning saidgenerating means to generatein-phase energy at said frequency, control means vconnected to said-generating means for timing the initiation of the radiation of saidiii-phase energy and for determining said time interval, -said controlmeans comprising a second wave generating means for generating aplurality -of out-of-phase voltages equal in number to the number ofsaid subordinate antenna arrays, the time-phase between vtwo successivevoltages of said out-ofphase voltages being substantially equa1 -to thetotal variation in space-phase of a wave radiated -by any antenna over adistance equal to the spacing `between two adjacent antennas, one ofsaid out-of-phase voltages controlling only the wave generating meansconnected to the antennas of one subordinate antenna array whereby theinitiation of radiation from one antenna follows the initiation of`radiation from an adjacent antenna by said time interval to produce awave in space having a length equal to said predetermined wavelength.

6. A directional wave propagating system in accordance with claim 5,wherein said control means also comprises a wave blocking means, saidblocking means comprising generating means for generating a secondplurality of out-of-phase voltages, the phase relation between thefirstnamed plurality of out-of-phase voltages and said second pluralityof out-of-phase voltages being such that no more than a given number ofsaid antennas are radiating simultaneously.

'7. A wave propagating system comprising a plurality of antennasarranged in lineal array in a fixed direction and means for energizingsaid antennas successively whereby the frequency of a space wave variesdirectly as the cosine of the angle between the direction of said arrayand the direction of propagation of said space wave.

8. A wave propagating system comprising a plurality of antennas arrangedin lineal array, and means for energizing said antennas in phase with avoice modulated high frequency wave successively one after the other,said means comprising a modulating sweep voltage generator and ablocking voltage generator, the phasing of said sweep voltage and saidblocking voltage being such that the time-phase at which any twoadjacent antennas are energized is substantially equal to the totalvariation in space-phase of a wave radiated oy any one of said antennasover a distance equal to the spacing between said adjacent antennaswhereby a plurality of space waves of different carrier frequencies buthaving the same modulation are radiated in a vertical plane passingthrough said array.

9. A radio direction finding system comprising a rotatable group ofantennas arranged in a predetermined array, antenna conditioning meansconnected to said antennas to condition said antennas for successivewave translation, a non-directional wave translating means, controlmeans for timing the operation of said conditioning means and formodulating said non-directional wave translating means, combining meansfor combining the output of the first-named wave translating means andof said non-directional wave translating means, and an indicatorconnected to said combining means for indicating the direction of areceived signal.

10. A radio beacon comprising a plurality of antennas arranged in apredetermined array, antenna conditioning means connected to saidantennas to condition said antennas for successive wave radiation,control means for timing the operation of said conditioning meanswhereby a plurality of waves lof different frequencies are radiated fromsaid array, the frequencies of said radiated waves varying as a functionof the angle between the direction of said Yarray and the directions ofpropagation of said radiated waves, a separate antenna, means forenergizing said separate antenna at a frequency such that the resultingradiated wave therefrom is equal to the frequency of one of the wavesradiated from said antenna array.

11. A radio beacon comprising a rst wave transmitting system comprisinga plurality of lantennas in lineal array, antenna conditioning meansconnected to said antennas to condition said antennas for successivewave radiation, control means connected to said conditioning means fortiming the operation of said conditioning means to initiate theconditioning of one of the antennas while discontinuing the conditioningof another of the antennas, a second wave transmitting system comprisinga plurality of antennas in a second lineal array, a second conditioningmeans connected to said antennas of said second array to condition theantennas of said second array for successive wave radiation, a secondcontrol means connected to said second conditioning means for timing theoperation of said second conditioning means to initiate the conditioningof one of the antennas of said second array while discontinuing theconditioning of another of the antenna thereof, and a high frequencypower source connected to both of said conditioning means for producingradiation from the antennas thus conditioned to produce interferencepatterns in space, said patterns having at least one direction in whichthe resultant radiated energy is substantially zero.

12. A radio beacon in accordance with claim 11 wherein the first-namedlineal antenna array and said second lineal array are positioned atright angles to each other.

13. A wave communication system comprising a plurality of antennasarranged in lineal array, means for energizing said antennas in phasewith a voice modulated high frequency wave successively one after theother, said means comprising a modulating sweep voltage generator and ablocking voltage generator, the phasing of said sweep voltage and saidblocking voltage being such that the time-phase at which any twoadjacent antennas are energized is substantially equal to the totalvariation in space-phase of a wave radiated by any one of said antennasover a distance equal to the spacing between said adjacent antennaswhereby a plurality of space waves of different carrier frequencies buthaving the same modulation are radiated in a vertical plane passingthrough said array, a receiving system located at a distance from saidantenna array, said receiving system comprising a receiving antenna anda receiver, said receiver having a plurality of frequency selectingmeans, each of said selecting means being tuned to select a differentone of said space waves of different carrier frequency, separatedetecting means connected to each selecting means for detecting saidvoice modulation and means to combine the output of said detectingmeans.

14. A wave communication system comprising a transmitting antenna fortransmitting a modulated wave having a single carrier frequency, areceiving system, said receiving system comprising a plurality of spacedantennas arranged in a predetermined array, antenna conditioning meansconnected to each antenna of said array for conditioning same to operatesuccessively for wave translating purposes, control means for timing theoperation of said conditioning means to initiate the conditioning of oneof said antennas while discontinuing the conditioning of another of saidantennas whereby said carrier Wave of single frequency is translatedinto a wave having a frequency spectrum, an amplifier connected to saidantenna array for amplifying the energy in said frequency spectrum, aplurality of selector means connected to said amplifier for selectingfrom said wave having a frequency spectrum a plurality of Waves ofdifferent frequency, and detecting and combining means connected to eachof said selector means for reproducing said modulation.

15. A Wave communication system in accordance with claim 14 furthercomprising a scanning frequency receiver and an oscillograph connectedto said amplifier for determining the Waves having the maximum energy.

16. The method of producing in space a spectrum of frequencies varyingfrom a maximum in one direction to a' minimum in another direction,comprising sequentially radiating from separate origins a plurality ofin-phase electro-magnetic waves.

17. The method of producing the effect of a single antenna movingthrough space, comprising successively conditioning for translation ofwave energy a plurality of similar antenna systems spaced inA apredetermined array,

18. In a communication system, the method of reducing the effects offading, comprising transmitting wave energy in the form of a modulatedcarrier wave, said carrier Wave having a frequency which varies with thedirection of wave transmission, making an energy collection of at leasta portion of said Wave energy, selecting a portion of said collectedenergy, said selected portion having a plurality of predeterminedfrequen.. cies, and detecting and combining said selected portions toreproduce said modulation.

19. In a communication system, the method of reducing the effects offading, comprising transmitting wave energy in the form of a modulatedcarrier wave of single frequency, making an energy collection of atleast a portion of said wave energy While simultaneously translating thesingle frequency of said wave portion to a frequency spectrum, selectingfrom said spectrum energy portions each having a predetermined frequencyand detecting and combining said selected energy portions to reproducesaid modulation.

, HENRI G. BUSIGNIES.

